Effects of CO₂ doubling, warming, and light drought stress on root growth and nitrogen uptake of winter wheat

Objectives Root system is the major organ of crop for nitrogen uptake. Researches on influences of CO₂ doubling, warming, light drought stress and their interactions on root growth and nitrogen uptake can provide a scientific strategy for crop nutrient management to cope with climate change.

Methods A pot experiment was conducted using winter wheat (Triticum aestivum L.) as test materials in artificial climate chambers. Four climate scenarios were established as follows: the controlled experiment (atmospheric CO₂ concentration 400 μmol/mol+normal ambient temperature, CK), doubled CO₂ (800 μmol/mol+normal ambient temperature, ECO₂), elevated temperature (400 μmol/mol+elevated temperature by 4℃, ETem), and doubled CO₂ and elevated temperature (800 μmol/mol+elevated temperature by 4℃, ECO₂+ETem) , meanwhile, each climate scenario included two water conditions, i.e., sufficient water supply (80% of field capacity) and light drought stress (60% of field capacity). The responses of root growth (root biomass, root to shoot ratio, total root length, root total surface area, and total root volume) and nitrogen uptake of winter wheat were investigated. Further, the relationship between nitrogen uptake and root growth was analyzed.

Results 1) Effects of CO₂ doubling on root growth of winter wheat at different growth stages were insignificant. Increasing temperature by 4℃ and light drought stress inhibited root growth at both anthesis and grain filling stages (P<0.05) . 2) The combination of CO₂ doubling, warming, and light drought stress inhibited root growth of winter wheat (P<0.05), while the synergistic effects of warming and light drought stress inhibited root growth. 3) CO₂ doubling decreased root nitrogen concentration of winter wheat at the grain filling stage (P<0.05), while had no significant effect on shoot nitrogen concentration. Increasing temperature by 4℃ increased the root and shoot nitrogen concentration at each winter wheat stage; light drought stress increased root and shoot nitrogen concentration. The interaction of CO₂ doubling and warming affected root nitrogen concentration; warming and light drought stress enhanced root and shoot nitrogen concentration (P<0.05). However, the interaction of CO₂ doubling and light drought stress and CO₂ doubling, warming, and light drought stress did not affect root and shoot nitrogen concentration (P>0.05) . 4) The responses of root and shoot nitrogen accumulation to CO₂ doubling, warming, light drought stress, and their interactions had the same trend as root morphological indexes. There were positive correlations between root nitrogen accumulation and the morphological indexes of winter wheat.

Conclusions In this experiment, warming and drought stress synergistically inhibited root growth of winter wheat. CO₂ doubling did not affect root and shoot nitrogen uptake across the growth stages of winter wheat. In contrast, warming and drought stress increased the root and shoot nitrogen concentration but decreased root and shoot nitrogen accumulation, and warming is considered the dominant factor affecting the nitrogen uptake of winter wheat.